Dealloc not called changing tab

问题

Let's suppose to have a tab bar controller with two tabs, A and B, where A is a navigation controller.

When the user is in A, he can push A1 and then A2, which are both view controllers. A back button on A2, performs:

[self.navigationController popViewControllerAnimated:YES];

which correctly triggers the dealloc method on A2.

If the user is in A2 and then switches to tab B, I need the dealloc method to be called on A2; therefore I've implemented the following method in the TabBarController:

- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController {
    UINavigationController *nc = (UINavigationController*)tabBarController.selectedViewController;
    [nc popToRootViewControllerAnimated:YES];

    return YES;
}

but in this flow the dealloc method of A2 is never called! How is it possible that popping from A2 to A1 it works, whereas changing tabs the view controller is not deallocated?

Thanks for any hint!

DAN

回答1:

dealloc is only for removing observers and freeing memory -- when or if it is called is up to the runtime

e.g.
think of the cases of release vs. autorelease (influence when it is called) or if you terminate an app (not called at all)

instead on relying on dealloc, write a method you explicitly call.. e.g. something like stop or finish or cleanup

or... use viewDidDisappear.

-- in any case, don't rely on dealloc

回答2:

It seems that didSelectViewController is triggered before the tab controller has switched to the destination tab. Therefore the execution of the method popToRootViewControllerAnimated correctly pops all the view controllers, but can't really release the visible one, as it is currently being depicted by the app.

To achieve my result, I've figured out the following solution. In the viewDidAppear method of all the view controllers which correspond to the first view controller for each tab, I execute popToRootViewControllerAnimated (all of them are navigation controller).

来源：https://stackoverflow.com/questions/18508425/dealloc-not-called-changing-tab